Seedling in the Rhynie chert – a less-common sight

Germinating spores and subsequent growth stages up to adult gametophytes* have been documented for the most abundant plants in the Rhynie chert, Aglaophyton and Rhynia [1,2]. (One related publication involves a misinterpretation, see Rhynie Chert News 8. ) Still obscure are the early stages of the sporophyte generations. This makes any one of the rarely seen early stages of plant growth an object of special interest.Early growth stage of a Rhynie chert plant

Figure: Early growth stage of a Rhynie chert plant, height 0.8mm, with rhizoids.
           Note the orientation of the cells on the left, possibly indicating the onset of sideward growth.

Sub-millimeter-size blobs with cellular structure are occasionally seen in the chert. If they bear rhizoids, as in the present case, they can be identified as early stages of growth. Lucky incidences providing optimal cuts are obviously rare, and in fact this one is the only own find of this kind. The tiny baby plant with rhizoids seen here was unexpectedly found in a big chert sample with abundant Aglaophyton and a few Rhynia.
The orientation of the cells on the left seems to indicate a beginning sideward growth. Hence the object could possibly be an early stage (protocorm) of the Rhynia gametophyte (named Remyophyton) whose variable shape and sideward growth is pictured in [2]. 
The present find can serve as an encouragement to look for more tiny objects possibly representing early stages of either gametophyte or sporophyte of any Rhynie chert plants whose adult stages are well known.
Annotation: The life cycle of the Rhynie chert plants involves alternating generations of short-lived smaller gametophytes and sturdy sporophytes, similar as with extant ferns. The gametophytes of the Rhynie chert plants, which come in male and female versions, produce sperm and egg cells, respectively. The sporophyte, which is the "proper" plant, grows from a fertilized egg cell, probably while the  gametophyte wilts and decays. Gametophytes are seldom seen in the chert, probably because of their short life and fast decay. Gametophytes have been given names different from the related sporophytes.

H.-J. Weiss      (2008)

[1] W. Remy, R. Remy: Lyonophyton rhyniensis …,
     Argumenta Palaeobotanica (Münster) 6(1980), 37-72, Tafel 7-13,.
[2]  H. Kerp, N.H. Trewin, H. Hass: New gametophytes from the Early Devonian Rhynie chert,
     Trans. Roy. Soc. Edinburgh, Earth Sciences 94(2004 for 2003), 411-28.

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